There are many good alternatives if you are willing to pour a little
money into this hobby (e.g.Sproutly). However I've maybe
found one of the crustiest methods of always having a fresh batch of
sprouts ready; using old milk cartons.

Take a couple of spoonfuls of seeds and let them rest in some lukewarm
water over night.

Clean out an old milk carton and cut it according to the image below.

Fill it with seeds. Put it on a tray and stash it away in some dark place.

Water twice a day.

Wait approximately a week, cut it open and enjoy your sprouts.

This method works surprisingly well for me. For some reason other
methods are hit and miss. So far I've had great luck with mung beans,
green lentils and black beans and I'm looking forward to trying other
things as well.

My partner prefers their coffee with soy milk so we always have a steady
supply of milk carton we otherwise would trow away so this a pretty nice
way of "reducing waste".